Module 4 - Plate Techtonics

Main sources of energy on earth

• External Solar Energy-bio geological cycle

• Internal geothermal heat (will stop after about 8 million years)

What does internal geothermal heat do

• melts rocks

• made volanos

• moves continents

plate techtonic theory

Earth’s surface is divided into a large series of plates that move around allowing continents to change position

who published the idea of contential drift

Alfred Wegner - 1912

What did Alfred Wegner propose?

Proposed pangea 

•  Supercontinent – earths cotenenial blacks or cartons to form a single land mass 

• Suggested that continent moved but plowing through the sea 

Reasons why Alfred suggested the idea of Pangea

• Continental shape  

• Glacial deposits of Gondwana: 

  • Distributions suggest southern continents formed single landmark in the past

• Similar land structure  (ex. Material found) 

• Similar rocks, fossils and structure on both sides of the Atlantic 

• Animals could not have travelled ocean and existed on same continents

how was the platethectonic theory tested

• Sonarwas used to map out ocean floor which proved that the Sea floor mountain system was formed by tectonic plates

What did hess discover 1962

• sear floor spreading created mid ocean ridges

• proposed that mantle mountain material may be coming out or subducting (crust is going into the mantle)

Geomagnetism

Study of the Earths magnetic field, including it’s origin structure and changes over time

Earth’s Magenetic field

vector quantity- strength and direction

How much do the magentic poles move

• 1100 km between 1831 and 2001

• since 1970 - acceleratied more thant 40km/year

Periodically the Earths magnetic field __

flips

• Noth pole → south pole

  • reversed polarity

Magnetic north has been present for…

780 000 yrs

Last documented magnetic pole reversal

330 years ago

Why do magnetic poles reverse

1. Based on behaviour of outer core  

2. Caused by fluctuation of the core 

3. Earths spinning core – produces magnetic reveral after 35 000 years of stimulated time 

How long does it take or reversal to occur

• abt 5000 yrs (1,000-8,000)

What would happpen in a reversal

• North end of compass would point south

  • humans would need to update navigation systems

• Weaker field

  • reduce protection from

    • solar wind (ionized particles from the sun)

    • solar flares

    • solar storms

    • mass ejections of plasma and gas

Impacts of a weaker magnetic feild-magentic pole reversal

• cause intense heating, expansion of upper atmosphere

• increased drag on satellites, decaying orbits

• interference with elecric signals

• ground currents can overlard power grid

How do rocks record magnetic files

• Magentic materails: - fixed in rock 

  • Solidifies 

  • Lithifies 

• Record magnetic field only at the time of cooling / lithification 

  • Can be reset by heating (igneous in particular)  

• Can be measured with a magnetometer 

paleomagnetism

study of ancient magnetic fiels of Earth preserved in rocks, sediments or archeological material

How was the idea of s>a floor spreading tested^

• Magnetometer surveys of the ocean floor identified patterns of anomalies on each side of MORS  

• Patterns matched patterns of magnetic reversals  

• Confirmed formation of sea floor and MOR's and movement away from the ridges 

Oldest recorded sea floor

• 400 million years

types of plate boundaries

1. Convergent Boundaries

2. Divergent Boundaries

3. Transform Boundaries

Divergent Boundaries

• Where plates move away from one another (contential or oceanic)

• Create new ocean Bains, new oceanic crust 

• Involves:  

  • thinning: (forces coming from both sides) 

  • rifting: (valley deep enough to let sea water to enter, maga enters 

  • Extension: plates move apart 

divergent boundaries are associated with…

• volcanism and shallow focus earthquake

Convergent boundaries

• Two plates move toward each other

• Ocean plate is denser and subducting into to mantle

Convergent boundaries are associated with…

• Shallow, intermediate or deep earthquakes 

• Partial melting creates silica-rich(andesitic) magma, explosive volcanos ex cascades. 

• Creates mineral deposits – very mineral rich 

Albedo

• property of a material that determines how much sunlight will be absorbed by a material

Ocean- Ocean coliding convergence

• Most dense plate subducts (colder, older, plate) 

• Form deep trenches and Island arc volcanoes 

Contenential- contenential crust colision

• obduction

subduction

where one techtonic plate moves under another

obduction

tectonic process where oceanic dense crust thrusts up and over lighter continental crust

Transform Boundaries

• Two plates sliding with one another, associated with shallow focus earthquakes  

• Often link sections of divergent or convergent margins